Method

1. Squeeze out any extra moisture from the grated courgette and carrot, then place in a bowl with all the other burger ingredients (apart from the spray oil), adding a generous grinding of pepper. Mix together thoroughly. 
    
2. Divide the mixture into 4 portions and shape into large, fairly thin burger patties. Chill in the fridge for at least 2 hours, or overnight.
    
3. When you’re ready to cook your burgers, mix together the yoghurt and harissa and set aside. Halve and toast the wholemeal burger buns.
    
4. Preheat the grill to high. Spray a baking tray a few times with oil and place the burgers on the tray. Spray the top of each burger a few times with oil. Cook under the hot grill for 5–6 minutes on each side, until nicely browned.
    
5. Spread the harissa yoghurt on the bottom of each burger bun, add a burger, then top with a tomato slice and some lettuce. Pop the lid on and tuck in.